EP0304881B1 - Touch system for coordinate measuring apparatus - Google Patents

Description

The invention relates to a probe system for coordinate measuring machines, with a probe delivering a probe signal, which has a receptacle for exchangeably attached styli.

Switching-type probes deliver a pulse-shaped output signal at the moment when the shaped probe body touches the workpiece to be measured on the stylus of the probe. A probe of this type is described for example in US-A 41 77 568. To increase the accuracy of the detection of the probing process, this known probe has a piezoelectric sensor which responds even with a very small probing force and thus when the workpiece is first touched, and supplies a signal which is used to record the measured values read from the scales of the coordinate measuring machine at this moment serves. A second signal pulse is generated when the movable stylus carrier moves away from its rest position as the probing movement continues. This second pulse serves to verify the first probing pulse and to discriminate against interference pulses which are caused, for example, by vibrations in the machine.

Different stylus combinations can be attached to the movable stylus holder of this known probe head with the aid of a changing device, as described in US Pat. No. 4,637,119 and in brochure No. 60-20-027e with the title "Probe Changing Systems" (note III / 85) by the applicant.

With this known touch probe, not all measuring tasks occurring in practice can be solved satisfactorily. For measuring tasks that require very long or very heavy stylus combinations, in connection with high Accelerations when moving the probe head on the problem that the stylus carrier is lifted out of its storage and already pretends a probing process when starting or braking.

To solve measuring tasks that require large stylus lengths, it is known to provide a large number of small switching probes instead of a central probe that carries different stylus combinations, which have only a very short stylus and are even attached to the coordinate measuring machine via appropriate distributors or extensions. Such a touch probe is described, for example, in German patent application DE-A-36 34 689 and the corresponding US patent application Ser.No. 105 825 and in the trade fair information "Microtechnic 86" from the applicant (brochure no. 60-25-004-d, printed note XI / 86). As can be seen from Figures 4 - 6 on pages 12 - 13 in the mentioned measurement information, these small switching probes with a smaller diameter are attached to the coordinate measuring machine via a kink that acts as a collision protection. This collision protection has a switch that responds in the event of a collision and is connected to the control of the coordinate measuring machine.

The collision protection is, however, preloaded with a very high spring force in comparison to the preloading of the stylus carrier in a probe head of the first-mentioned type. This is necessary so that the zero position of the probe combinations attached to them with their relatively large mass is ensured even if relatively high tilting moments act on the collision protection due to their off-axis attachment.

The system described above with many small switching probes and a collision protection provided for it is relatively complex and increases the price of the coordinate measuring machine equipped with it. In addition, a simple switch between the two systems is not possible because For this purpose, the complete system with the collision protection was dismantled and a switching button of the first type would have to be installed. Such conversions are always associated with a subsequent recalibration of the touch probes.

It is the object of the present invention to design a touch probe of the type mentioned at the outset in such a way that, with as little effort as possible, even large stylus extensions can be attached and moved at high speed.

This object is achieved by a touch probe and a method for its operation with the features specified in the characterizing part of claims 1 and 9, respectively.

These measures combine the advantages of the two touch probes described in the prior art, a rapid change between the two systems being possible at the same time. So the e.g. Switching central pushbutton, with which a multitude of different measurement tasks can already be solved, when changing to the system with several small switching probes on the machine and serves as collision protection in this operating mode. The change itself to this two-stage system can be done without lengthy conversion work simply by attaching the small switching probe heads of the second type to the central pushbutton instead of the star stylus instead of the star stylus.

For this purpose, it is advantageous to integrate contacts for transmitting the probe signals of the second probe into the stylus holder in the first probe. These contacts are not only used to transmit the probe signals of the second probe to the cable connection on the first probe with the measuring machine but can also serve to recognize the replaced part, ie a rigid stylus or the second probe, and automatically switch to the required operating mode.

While the central probe head is operated in a conventional manner when the rigid probe is replaced, after the second probe system has been replaced there is a switchover to the signal transmitter in this second probe system and at the same time the pretension with which the stylus holder in the first probe is in its rest position is pressed, for example increased by a motor-compressed spring. The first probe then has collision protection functions and the outputs of its signal transmitters are advantageously forwarded to the corresponding control part in the coordinate measuring machine for the purpose of stopping the drives of the measuring machine in the event of a collision.

Fig. 1

ist eine vereinfachte Darstellung des erfindungsgemäßen zweistufigen Tastsystems bei eingewechseltem starren Taster;

Fig. 2

zeigt das zweistufige Tastsystem bei eingewechseltem schaltenden Tastkopf;

Fig. 3

ist ein Blockschaltbild der in Verbindung mit dem zweistufigen Tastsystem aus Fig. 1 bzw. Fig. 2 verwendeten Elektronik.

Further advantages of the invention result from the following description of an exemplary embodiment with reference to FIGS. 1-3 of the accompanying drawings.

Fig. 1

is a simplified representation of the two-stage touch probe according to the invention with a fixed probe;

Fig. 2

shows the two-stage touch probe with a switched switching probe;

Fig. 3

is a block diagram of the electronics used in connection with the two-stage touch probe of Fig. 1 and Fig. 2.

In Fig. 1, (1) denotes the housing of a central probe of the first type. This housing can be fastened, for example, to the quill or the cross arm of a coordinate measuring machine via connecting elements (not shown in more detail).

There is a three-point bearing inside the housing, on which the movable part (2) of the probe rests. Only the two bearing balls (7a and 7b) of this three-point bearing are shown. The bearing balls form an electrical switch, which indicates the lifting of the movable part (2) from its bearing. The electrical connection to this switch is labeled (S7).

The movable part (2) of the probe (1) is pressed into its bearing by a spring (3) which is supported against a plate (4) which is straight in the housing (1) and axially adjustable by a threaded spindle (6). The threaded spindle (6) is driven by a motor (5) in the upper part of the housing (1).

The end position of the area in which the spring (3) can be adjusted is marked by two microswitches (16 and 17) in the housing (1) against which the plate (4) moves.

A stylus receptacle (8) is fastened to the movable part (2) of the probe head with the aid of a connection shown in simplified form as a screw (9). A piezoelectric sensor (10) is arranged between the stylus receptacle (8) and the supporting part (2), the signal of which is used for probe detection. Inside the receptacle (8) there is an electromagnet (11) with a permanent magnetic core. With the help of this known changing device, the fastening part (13) of a rigid stylus (14) is pulled against a three-point bearing, which is again formed from balls (12), on the underside of the stylus holder (8). (15) denotes the ferromagnetic core in the holding part (13) for the stylus (14).

Inside the stylus receptacle (8) there are also contact pins, two of which (18a and 18b) are shown. The function of these styli will be explained with reference to FIG. 2. When the rigid switch is inserted, as in 1, the contacts (18a and b) are grounded.

2 is instead of the rigid stylus (14) a complete "small" switching probe (21) with a much smaller diameter compared to the probe (1) via an intermediate piece (19) to the stylus holder (8) switching probe (1).

In principle, the probe (21) has the same structure as the probe (1). It has a movably mounted part (22) which is pressed by a spring (23) against a three-point bearing which determines its zero position. Here, too, the bearing balls (27) form an electrical circuit. The stylus (24) of the probe (21) is connected to the part (22) via a second piezoelectric sensor (20) placed in between.

The probe (21) is screwed onto the extension piece (19) with the aid of a union nut (29). This has a ferromagnetic insert (25) at its other end and is pulled by the magnet (11) in the stylus holder (8) of the central probe (1) against the bearing (12) of the stylus changing device.

The extension piece (19) contains mating contacts (28a, b and 26a, b) on both sides, which send the signals from the piezoelectric sensor (20) and the switch formed from the bearing balls (27) to the mating contacts (18a, b) in the stylus holder Forward (8) in the probe (1).

1, the spring (3) is in the partially relaxed state and exerts only a small force of approximately 0.2 N on the stylus holder (2). In this position of the spring, the probe (1) operates in the conventional manner as a switching probe, the set spring force determining the contact force exerted by the stylus (14) on the workpiece to be measured.

When the switching probe (21) according to FIG. 2 is inserted, the spring (3) in the probe (1) is compressed more. The stylus holder (2) rests on its bearing with a force of approx. 50 N. In this setting, the probe (1) only has the function of collision protection, i.e. the part (2) snaps out of the bearing when the probe (21) or the probe extension (19) is inadvertently driven against an obstacle. The actual probing in the setting according to FIG. 2 takes place with the aid of the stylus (24) of the "small" probe (21).

Between the two operating modes according to FIGS. 1 and 2, an electronic arrangement (30) is used to switch the connection cables of the motor (5), the limit switches (16 and 17) of the switching bearing (7) and the alternating magnet (11 ), and the contact pins (18a, b) are supplied. This arrangement (30) is shown in FIG. 3 and is described in connection with the following explanation of the functioning of the touch probe: The arrangement (30) contains the motor control (37) for the motor (5) in the probe (1). The motor controller (37) is connected to a microprocessor system (36) and receives from it the control signals for setting the spring force of the spring (3). The motor control (37) is also connected to the limit switches (16 and 17), which report that the upper or lower adjustment limit for the spring has been reached.

The microprocessor (36) simultaneously controls the switching of the key signals between the first and the second probe via the two relays (34 and 35). When switching, the relay (35) either places the piezoelectric sensor (20) in the probe (21) or the piezoelectric sensor (10) in the probe (1) at the input of an amplifier and pulse shaper stage (33). In the operating mode according to FIG. 1, the relay (34) places the switch (S7) of the bearing in the probe (1) at the input of a trigger stage (32). 2, the relay (34) connects the circuit (S7) to the collision protection circuit (39) of the coordinate measuring machine.

At the same time, the circuit (S27), i.e. the switching bearing in the second probe (21) at the input of the trigger circuit (32). The outputs of the circuits (33 and 32) are combined in a coincidence circuit (31), from which the actual pulse sequence is passed on to the coordinate measuring machine. This part of the circuit is known per se and is already part of the electronics of the probe mentioned at the beginning of the prior art.

The changeover process can either be controlled by the coordinate measuring machine via the microprocessor (36), or initiated by the latter itself if a possibility of recognizing the replaced part is provided. The cable connection shown in broken lines in FIG. 3 between the piezoelectric sensor (20) and the microprocessor (36) is used for this purpose. Since the contacts (18a and 18b) are grounded when the rigid pushbutton (14) is replaced according to Fig. 1, it can be determined, for example, by querying the internal resistance of the connected circuit, whether a rigid stylus (14) or a small switching pushbutton ( 21) is on.

a:

Verwendung zur Tastsignalgewinnung und

b:

Verwendung als Kollisionsschutz bei angesetztem zweiten Tastkopf

umschaltbar ist. Schließlich ist es auch möglich in Umkehrung dieses Prinzips einen kleinen messenden Tastkopf an einen schaltenden Zentraltastkopf anzusetzen.2, a single "small" switching button (21) is connected to the central probe (1) via the extension piece (19). However, it is clear that several small probes can also be attached via connecting pieces (19) which are designed as distributors. At this point reference is made to the patent application P 36 34 689.6 already mentioned at the beginning. It is also possible to use a probe of the measuring type or a universal switch instead of the switching central switch (1), which is between the two operating modes

a:

Use for tactile signal acquisition and

b:

Use as collision protection when a second probe is attached

is switchable. Finally, in reverse of this principle, it is also possible to attach a small measuring probe to a switching central probe.

Claims (12)

1. A probe system for coordinate-measuring instruments wherein a probe head includes a receptacle (8) for interchangeably mounted probe pins (13) and a signal output for producing a probe signal, the improvement wherein an auxiliary probe head (23) is provided having smaller dimensions compared to said first probe head, said auxiliary probe head being adapted for mounting to said receptacle (8) and having also a signal output producing a probe signal, and associated electronics (30) connected to said signal outputs of both probe heads, when said auxiliary probe head is mounted, for switching between two modes, in which modes the signal outputs for the probe signals either of said first probe head or of said auxiliary probe head are connected to the coordinate measuring instrument.
2. The probe system of claim 1, wherein said electronics (30) is connected to a device (4-6) for varying the biasing force of the first probe head (1).
3. The probe system of claim 1, wherein both probe heads (1, 21) are of the switching type and each of them contains a contact-responsive sensor (10, 20) and a switch (S7) responsive to deflection of the probe pin.
4. The probe system of claim 2, in which said switch (S7) responsive to deflection in the first probe head can be connected to circuit means (39) for stopping the coordinate measuring instrument carrying said probe system.
5. The probe system of claim 1, wherein said receptacle (8) includes electrically operated chucking means (11) and contacts (18a, b) for outputting transfer of the output signal of said auxiliary probe head (21).
6. The probe system of claim 1, wherein said associated electronics (30) includes electronic means for recognizing the part mounted to said receptacle.
7. The probe system of claim 1, wherein an extension member is provided for connecting the auxiliary probe head (21) to said receptacle (8) at the first probe head (1).
8. The probe system of claim 7, wherein said extension member comprises separate means for mounting each of a plurality of auxiliary probe heads simultaneously.
9. A method of operating a probe system for coordinate-measuring instruments comprising two probe heads (1, 21) having different dimensions, characterized by the fact that the second probe head (21) which has the smaller dimensions is mounted to the deflectable probe-pin receptacle (8) of the first probe head (1) having the larger dimensions; that the probe signals (S27, piezo 20) of the smaller probe head are fed to the coordinate-measuring instrument instead of the probe signals (S7, piezo 10) of the larger probe (1) and that the biasing force of the deflectable receptacle (8) of the first probe head is increased.
10. A method according to claim 9, characterized by the fact that the probe signals (S7) of the first probe head (1) are used for controlling a collisions-protection circuit (39) of the coordinate-measuring instrument, as long as the smaller probe head is mounted.
11. The probe system of claim 1 wherein the first probe head is a measuring probe and the second probe head is a probe of the switching type.
12. The probe system of claim 1 wherein the first probe head is a switching probe and the second probe head is a probe of the measuring type.

Images